Problem: What is the greatest common factor of $20$ and $24$ ? Another way to say this is: $\operatorname{gcf}(20, 24) = {?}$
The greatest common factor is the largest number that is a factor of both $20$ and $24$ The factors of $20$ are $1$ $2$ $4$ $5$ $10$ , and $20$ The factors of $24$ are $1$ $2$ $3$ $4$ $6$ $8$ $12$ , and $24$ Thus, the greatest common factor of $20$ and $24$ is $4$. $\operatorname{gcf}(20, 24) = 4$